Overload protective device.



E. I. W. ALEXANDERSON.

UVERLOAD PROTEUTIVE DEVICE.

APPLICATION FILED MAY 15, 1905.

Patented Apr. 12, 1910.

1 m WH m TL m T A w Nd w Ma 1 Z L 5 m E m Q P Q 5 :LF 4 $4 3 Z 4: H z WJG WZ Z W BY E. F. W. ALEXANDERSON. OVERLOAD PROTECTIVE DEVICE. vAPPLIOAIION FILED MAY 15, 1905.

954,845. Patented Apr. 12, 1910.

2 SHEETSSHEET 2.

WETNESSES :NVENTOR Atty ' UNITED STATES PATENT cl rion ERNST F. W.ALEXANDERSON, OF SCHENECTADY, NEW YORK, ASSIGNOB/ TO GENERAL ELECTRICCOMPANY, CORPORATION OF NEW OVERLOAD PROTECTIVE DEVICE. V V I To allwhom it may concern:

zinnnnson, a' subject of the King of Norway.

and Sweden, residing in Schenectady, county of Schenectady, and State ofNew York, have invented certain new and useful Improvements in OverloadProtective Devices, of which the following is a specification.

-My invention relates to overload protective devices for compound,self-exciting, alternating-current generators.

In its broadest aspect, my invention is applicable to any self-exciting,alternatingcurrent generator provided with compound. ing means such asseries transformers, but in certain ofits features my invention refersparticularly to an alternating-current generator compounded in themanner disclosed in a former patent, No. 789,476, issued to me May 9,1905, in which a resistance is placed in series with the shuntexcitation, and the secondary of the compounding series transformer isconnected in shunt to theresistance.

In its broadest aspeet,i'i1y invention consists of a protective deviceadapted upon an overload to cut the compounding means out of circuit, asby short circuiting the series transformer supplying the compoundingexcitation for the generator. Since a self-exciting compoundalternating-current generator can carry only a small" portion ofitsfu'll load ,when operating as a shuntmachine, owing to the largearmature reaction whichis presentjn alternating-current machines, cut

ting out the compounding means is as efi'ect-' ive in protecting thegenerator from an overload as opening the circuit would be; since as"soon as the compounding means is 'cut' out, the currentjinnnediatelyfalls to zero, so that no damage to the generator can 'Th'e reasonforthis appears For a critical load on which, the machine cannot builduporkoep its excitation. For DQC. shunt machines this criticalload isfar' beyond a reasonable overload butfor alternators it' may be insidethe normal-load. The machine will therefore lose its voltage and ourrentcompletely, until. the overload has Specification of Letters Patent.

Application filed May 15, 1905. Serial No.

is lower than would be the case if resistance 7 referencoto theaccompanying'drawings,"in

Pat

been removed. Thus, and inexpensive device-,'1t necessary to providesuch switches adapted to open cuit upon a large overload As has beenstated ab featuresmy invention refe the protection of a gener asdisclosed in my forme with a resistance conneeted'in'. or 's with theshunt excitation, and 'a compoundin g transformer connected inshunt tothe" re sistance. In its application to such an arrangement ofcompounding, my invention comprises the additional featnrefofldiscomnecting. one or both. terminals of the series transformer from theresistance, when shortcir'cuiting the transformer upon itself, andleaving the resistance in series with the shunt excitation. Thisresistance left in series with the shunt excitation, reduces the loadwhich the generator can carry when the series transformer is out out toa point that and series transformer were both short-circuited.

My'invention comprises a number of other featuresfwhich will appear fromthe follow-' ing specification and accompanying drawings, and which willbe more" specifically pointed out in the appended claimsl I Myinventionwill best'be understood by which c Figure 1 showsdiagrammatically the con nection's of an overload protective devicearranged in accordance with my invention and applied to a generatorcompounded in amanner disclosed in my former patent above referred to;Fig. 2 shows a plan view-of a protective device arranged in. accordancewitli1nyinvention and adapted for protectional detail.

Referring first to, Fig. 1, A represents the armature of analternating-current gen- "erato'r; This winding is shown as a three 100phase, bipolar, Gramme rmg winding, but 1t. will, of course, beunderstood that'my invention is applicable to a machine having anynumber of phases and of poles, and any well-known form of armaturewinding.

1 F represent the field coils, which are connected to the segments of acommutator C, on which bear a three-phase arrangement of brushes 1/ band I). The arrangement of commutator and brushes here illustrated isfully disclosed in my former patent No. 789,476, above referred to. Todescribe it briefly, it consists of a commutator having as many se mentsas the machine has poles, with a po yphase arrangement of brus esbearing thereon and connected to a polyphase source of excitation, aswill be hereinafterexplained. The segments have a length substantiallyequal to the distance between adjacent brushes, so that segment leavesone brush, it engages with another. If a three-phase current is suppliedto brushes displaced from each other 120 electrical degrees, a directcurrent will be supplied to the field wind armature leads.

ing. The brushes are connected to any suitable source'of shuntexcitation, in this case the source being indicated by an auxiliarythreephase winding a a and a carried by the armature. ph-ase of theauxiliary winding is connected to a commutator brush, while the otherter' minal is connected through resistances R and 1', etc, to a commonconductor 0. That,

is,.the' three phases are shown connected in Y. V

- "T T and T -represent three series trans fo1'niers,-,the primaries ofwhich are connected respectively in series with the main The secondariesof these transformers are connected across the ac sistances R R and Bthrough three switches or switch contacts S S and S and through theiractuating coils s and a respectively. Vith the series transform- 7 ersthus connected, the current flowing from the transformen,secondariesthrough the resistances R R andlttisproportional to the current in themain'leads, and consequently the voltage across the terminals of theseresistances due to this current flow is proportional to the .mainarmature current. Thus, if the "transformer secondaries are properlyconnected, at potentlal will be added'to the shunt excitation, due tothe auxiliary exciting Winding a, at and ct,

proportional to the main armature current.

In other words,"the proper compounding 1S 7 obtained, Itwill be noticedthat the'series transformers are so] connected relatively toheffphifsesfzof the" lary exciti-n I-od that the compounding "potentia'-added. the series transformers tojthe shunt e5:- -c1tation is at rightangles to the shunt excitation. Thisarrangementis for the purposecf-obtaining the proper compounding commutator One terminal of each'Fig. 3.

*ances r 1- and r are shown variable for the pur ose of adjusting'theexcitation of the mac ine in the usual manner.

The connections shown in Fig. l are ma1ntained as long as the machine isoperating If, however, an

under normal conditions. overload should occur, the current in theseeondary circuits of the series transformers would increase so as toactuate one or all of the magnet coils 8 s and 8 which would "thereuponoperate, as will be hereinafter explained, to shift the switches S, Sand S to the opposite contacts. This movement of the switchesdisconnects one terminal of the secondaries of the series transformsfrom the resistances R R and R and short-circuits the transformers uponthemselves.

Consequently, not only is the compoundin effect of the seriestransformers remove from the field circuit of the generator but,

furthermore the resistances R, R and R are left in series with thesource ofshunt excitation, so that .the resistance of the excitingcircuit is left unchanged, and the over load is beyond, the criticalload of the shunt machine. The armature current conse' guently falls tozero and the machine is as ully protected against damage from anoverload as though its armature circuit had been completely broken; andthus protection is obtained by means of switch contacts which may besimple and inexpensive, since the power controlled by them is atalltimes comparatively small.

I have described the circuit connections for a system of compoundingarranged in accordance with my former patent. Obviously, my invention isapplicable to any other arrangementof compounding in which seriestransformers are employed. ,In every case it. is necessary only toconnect the figures-1 represents a suitable casing,-preferably ofmagnetic material inclosing the ac t-uating coils for the switchcontacts. Oneof these coils s is shown in cross sectionin' Thejcasing 1is provided with a suitable insulating cover 2,;on which are mounted theswitch'con'tacts S, S and S These contacts'oonsist of laminated brushes'carried by a block?) pivoted on suit-able sup; I ports 4. The block-3is pointed at its lower end and bears sgainst a spring '5, which pressesupwardly on the pointedend ofthe block. Withthis constructiomif theswitch contact is:-1n0vedin either-direction past'its midposition, thespriiig 5 tends to press'itfl forward to complete its movement, with a lv open-circuiting of the secondaries of the sesmall auxiliarycontacts'8, which are so ar-' ranged that when the switch contact ismoved from one position tothe other, one

contact 8 engages one of the stationary contacts 6 or 7 before the othercontact 8 leaves the other stationary contact. This arrangement is forthe purpose of preventingan ries transformers. The transformer isshort-circuited before its connection with the resistance is broken. Thefinal break is made by the auxiliary contacts 8.

, For operating the switch contact S automatically, the magnet coil 8 isprovided with a suitable core or plunger 9 carried inside a hollow tube10 and supported ad- 'justably by a screw 11 engaging-a screw thread onthe inner surface of the tube 10. VVhenan'overload occurs and the coil8' draws up' t e lunger 9, it strikes the lower end of a s incfie 12,whichis thereby raised so as to strike the pivoted block 3 with ahammer-blow and force it over to the position shown in Figs. 2 and 3.The series transformer is thus short-circuited in the manner heretoforedescribed. It will be seen that one or all of the switch contacts may beactuatedat a single time, according as the overload comes upon one'phaseor all the phases, since each switch contact is provided with its ownactuating coil.

. Iniorder to reset the switch contacts afterthey have oncebeen shiftedby their actuating coils, I provide a suitable "insulating handle 14carried by a hollow tube 16, which slides on a spindle 17, and isnormally li'eld raised against an adjustable nut 18 by the spiralspring-15. The lower part of the tube 16 moves" in a hollow tube '20,and is provided with a tongue 19, which moves in a slot in tube 20,and'serves as a guide to prevent the handle from twisting. The'han- 1ecarries three books 21, which, when the handle is depressed, are adaptedto engage the'blocks 3 of. the switch contacts and rock 'the blocks ontheir pivots so as to shift the switch contacts into engagement with thestat onary contact 7. Thus,

movement of the handle, allthe'switch con? facts that have, been triped, whether one en the handle .to. the position or all: ofthem, arereset. is released it ,is returne shown bythe string 15.

I do not desire 'tolimit myself to the par ticular construction andarrangement of by a single parts here shown, but aim in the appendedclaims to cover all n'iodifications m-h are within the scope of myinvention.

What 1 claim as new, and desire to secure by Letters Patent of theUnited States, is,

1. In coml'iination with a self-exciting alternating-current generatorhaving a field winding provided with a rectifying commutator, a sourceof shunt excitation connectcd to said commutator, a resistance in serieswith said source, a transformer having its primary connected in serieswith the armature of said generator and its secondany in shunt to saidresistance, and automatic means for short-circuiting said transformerand disconnecting it from said resistance whenthc armature current ofthegenerator exceedsa predetermined amount.

2. In combination with a self-exciting alternating-currciit generatorhaving a field winding provided with a rectifying commutator, a sourceof shunt excitation connected to'said commutator, a resistance in serieswith said source, a transformer having its primary connected in serieswith the armature of said generator and its secondary 1n shunt to saidresistance, a magnet wlnding in series with one of the windings of saidtransforn'ier, and a switch controlled by said 1nagnet winding andadaptedto short-circuitsaid transformer and to disconnect it from saidresistance.

3. In combiuationwith a self-exciting alternatingcurrent generatorhaving a field winding provided with a rectifying commutator and anauxiliary exciting winding carriedby the armature and connected to saidcommutator, a resistance in series withsaid exciting winding, a seriestransformer having its primary connected in series with the armaturewinding and its secondary in shunt to said resistance, a magnet winding.in series with said secondary, and a switch con trolled by said magnetwinding and adapted to short-circuit said transformer and to dis- Iconnect it' from said resistance.

4: In a protective device for a'fpolyphase circuit, a plurality ofmagnet windings supplied with current from the several phases ofsaidgcircuit, independent switches controlled by said magnet windingsand controlling said circuit, a single handle an ranged to resetsaidswitches simultaneously, g

and a spring-normally holding said handle out of engagement with saidswitches] 5. In combination, a resistance, a series ism transformerhaving its secondary winding in shunt to said resistance, and a switchhaving its contacts so constructed and. arranged that in its movement.it first short-circuits said secondary, then disconnects it'from saidresistance without breaking-the short circuit, and maintains theshort-circuit.

'6. In'combination, a resistance. a. series net Winding in serles withsaidsetondary-,

transformer having its seconda-lfy cpnnected v In witness whereof, Ihave hereunto set 111 shunt to. sand res stance, an ovrlcad magmy handthis 12th daypf May, 1905.

and a switch controlled by -said"r'xia gnet ERNST HEXANDERSON' windingand adapted by its movement first Witnesses:

to short-circuit said secondary and then to BENJAMIN B. HULL,

disconnect it from said resistance. HELEN ORFORD.

